Apparatus for continuous casting a metal strand shaped to provide concave surfaces

ABSTRACT

An apparatus is disclosed for supporting and shaping a quadrangular strand of metal with a still liquid core, emerging from a mold of a continuous casting machine. A first pair of rolls are spaced apart to support two oppositely facing surfaces of the strand, and a second pair of rolls are spaced apart to support and shape another two oppositely facing surfaces of the strand. Each roll of the second pair has equal end diameters smaller than a diameter midway between the end diameters and defines a convex peripheral surface which shapes the strand to form a pair of oppositely facing strand surfaces defining a continuous concave arch. The convex rolls are movable toward and away from each other between the first pair of rolls for supporting and shaping such strands of different widths.

United States Patent 11 1 Schoffmann [4 1 Aug. 19, 1975 [75] Inventor: Rudolf Schoffmann, Linz, Austria [73] Assignee: Allis-Chalmers Corporation,

Milwaukee, Wis.

[22] Filed: Jan. 2, 1974 [21] Appl. No.: 429,701

[56] References Cited UNITED STATES PATENTS 12/1970 Gallucci 164/282 3,583,473 6/1971 Strohschein et al. 164/273 R 3.7731199 11/1973 Rossi 164/89 FOREIGN PATENTS OR APPLICATIONS 1,492,047 7/1967 France 164/273 R 18,168 8/1898 United Kingdom 164/76 Primary Examiner-R. Spencer Annear Attorney, Agent, or Firm-Arthur M. Streich 5 7] ABSTRACT An apparatus is disclosed for supporting and shaping a quadrangular strand of metal with a still liquid core, emerging from a mold of a continuous casting machine. A first pair of rolls are spaced apart to support two oppositely facing surfaces of the strand, and a second pair of rolls are spaced apart to support and shape another two oppositely facing surfaces of the strand. Each roll of the second pair has equal end diameters smaller than a diameter midway between the end diameters and defines a convex peripheral surface which shapes the strand to form a pair of oppositely facing strand surfaces defining a continuous concave arch. The convex rolls are movable toward and away from each other between the first pair of rolls for supporting and shaping such strands of different widths.

2 Claims, 3 Drawing Figures APPARATUS FOR CONTINUOUS CASTING A METAL STRAND SHAPED TO PROVIDE CONCAVE SURFACES CROSS REFERENCE TO MY COPENDING PATENT APPLICATION A continuous casting machine mold for forming a strand of cast metal as described in this application but so forming the strand before the strand emerges from the mold, is the subject of my copending patent application entitled Mold With Two Convex Sidewalls For Continuous Casting Machines," Ser. No. 429,702 filed concurrently with this application.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an apparatus for supporting and shaping continuously cast slabs, billets and related products which have a basically guadrangular, normally rectangular, cross section. The operation of a continuous casting machine with an apparatus such as provided by this invention, involves charging a casting mold with liquid metal and precooling the metal in the mold for the purpose of forming a strand having a closed shell of solidified metal surrounding a still liquid core, with the strand leaving the mold and being supported and shaped after it has left the mold.

2. Description of the Prior Art It is known to those familar with this technology, and disclosed in my prior patents US. Pat. Nos. 3,589,429 of June 29, l97l and 3,710,847 ofJan. 16, 1973, that a strand with only a relatively thin shell of solidified metal is formed in the mold of continuous casting plants. Complete solidification of the strand occurs in the so-called secondary cooling zone after leaving the mold. The strand shell formed in the mold, due to its relatively thin walls and also due to the high temperature, is not able to resist the ferrostatic pressure of the liquid strand core enclosed by the shell. Therefore, supporting devices such as rolls, plates, lifting beams and similar devices have to be provided which prevent excessive bulging or tearing of the shell. The supporting devices provided have to be adjusted to accommodate the size strand being cast and must be precisely aligned with the mold which results in considerable adjusting and alignment work, especially for facilities which change cast sizes frequently. Also affected by frequent size changes is the total production rate of machines due to the interruptions in operating availability. The supporting devices may be damaged considerably during breakouts of the strand leaving the mold which causes additional repair costs.

Normally the rectangular cross section of the strand leaving the mold is determined by the shape of the exit cross section of the mold. For so-called slow casters and for continuous casting machines for strands with relatively small thickness, it is satisfactory sometimes to support the strand leaving the mold only on the wide sides, although small bulges due to the ferrostatic pressure may occur on the small sides. These small bulges may be acceptable in certain special cases.

For larger strand thicknesses as in the case of thick slabs, and also for so-called high speed casters as well as for essentially square strands, supporting devices are also necessary for the other two sides of the strand, that is for the narrow sides in the case of a rectangular format, as shown in U.S. Pat. No. 1,841,297 of Jan. 12, 1932 and US. Pat. No. 3,318,366 of May 9, 1967. Otherwise these sides of the strand would bulge excessively due to the ferrostatic pressure and cause danger of breakouts. The adjustment and alignment of the rolls supporting the narrow sides must'also be provided for since changing of strand width is much more common than changing of strand thickness.

Molds for casting strands having several crosssectional configurations, including molds with internal walls that are concave surfaces, are shown in the aforesaid U.S. Pat. No. 1,841,297 ofJan. 12, 1932, and US. Pat. No. 3,075,264 of Jan. 29, 1963.

SUMMARY .OF THE PRESENT INVENTION This invention relates to an apparatus for supporting and shaping a strand of metal with a still liquid core, emerging from a mold of a continuous casting machine. According to a preferred embodiment of the invention a first pair of rolls is spaced apart to support two oppositely facing surfaces of the strand, and a second pair of rolls is spaced apart to support and shape another two oppositely facing surfaces of the strand. Each roll of the second pair has equal end diameters smaller than a diameter midway between the end diameters and defines a convex peripheral surface which shapes the strand to form a pair of oppositely facing strand surfaces defining a continuous concave arch. This arch improves the total strength of the shell of the strand and especially the strength of the strand walls with the concave arch. This increase in strength will assure that bulging is prevented even if additional support for the strand walls is not provided beyond the convex rolls. Therefore, it is satisfactory, normally, to support the strand beyond the convex rolls only on the wide sides, which remain flat. The thrust required to produce the arch is transferred into the rolls supporting the strand shell on the wide sides. The same thrust also pushes the corners of the strand toward the outside so that they remain flat and parallel to the rolls supporting the wide sides of the strand which provides a uniform strand thickness over the entire width of the strand.

It is also a feature of a preferred embodiment of the present invention that the convex rolls are movable toward and away from each other between the first pair of rolls, for supporting and shaping such strands of different widths.

Other features of the invention that have been provided will appear from the more detailed description to follow with reference to an embodiment of the present invention shown in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. I of the drawing shows schematically a fragmentary cross section view of a strand fonning a slab, after leaving a mold according to teachings of the prior art;

FIG. 2 shows diagramatically a fragmentary side elevation cross-section view of a continuous casting machine mold, and support rollers for a strand emerging from the mold, according to the present invention; and

FIG. 3 of the drawing is a view taken along line III- -III in FIG. 2 and viewing the structure in the direction indicated by arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENT Before beginning a description of a preferred embodiment of the present invention, reference is made. to FIG. 1 which shows a fragmentary cross-section view of a strand of cast metal fonning a slab, after leaving a mold according to teachings of the prior art.

According to conventional teachings of the prior art, a slab 1 as shown in FIG. 1 emerges from a mold (not shown) with a strand shell 2 having relatively wide sidewalls 2a connected by a narrower end wall 212, enclosing a still liquid strand core la. As shown in FIG. 1, the narrow side 2b of the shell 2 is bulged to the outside by the ferrostatic pressure which causes the slab thickness to decrease from the desired value d to the actual value d and which may cause cracks 3 in the comer area 3a which in turn may cause breakouts of the liquid core.

Due to the reduction in thickness in the corner zones, support rolls (not shown in FIG. 1) for the wide sides will not be effective over the full width of the strand. Further, pinch rolls (not shown) cannot pull over the entire width which causes the pullout force to be reduced and which requires that a larger number of pinch roll stands be provided than would be necessary with perfectly flat sidewalls 2a or with a precisely rectangular cross section. The entire slab cross section is reduced by a certain amount; therefore, it is necesary to take safety precautions. The final shape of the slab also causes difficulties with reheating prior to the slab entering a rolling mill, and increases the danger of corner cracks in the first rolling pass, since the corner area is elongated due to the smaller thickness.

All thesedisadvantages are avoided by the present invention, as shown in FIGS. 2 and 3. FIG. 2 shows a mold =4 having a pair of end walls 5, and mold 4 has a pair of sidewalls 6 with only one of the sidewalls 6 being shown in FIG. 2. The sidewalls 6 may be wider than the end walls in order to cast a strand with a cross section such as will be described later with reference to FIG. 3. FIG. 2 shows the initial formation of a cast metal strand 12, having a shell comprising sides 12a, 12b and a liquid core 12c. Below the mold 4 strand 12 is supported by rolls 7 and 8 which will also be described with reference to FIG. 3.

Referring now to FIG. 3, a first pair of parallel support rolls 7 journaled in support arms 7a, are spaced apart from each other to engage and support the two relatively wide side surfaces 12a of strand 12. A second pair of parallel support rolls 8 are journaled in forked support arms 8a, and are spaced apart from each other toengage and support the two narrower side surfaces 12]) of strand 12. Each of the rolls 8 has equal end diameters smaller than a diameter midway between the end diameters and defines a convex peripheral surface to not only support the sides 12b of strand 12, but to also shape the sides 12b to define a pair of oppositely facing concave arches. Each of the forked support arms 8a may be connected to suitable hydraulic fluid pressure operable motors (not shown) for moving the convex rolls 8 toward and away from each other as indicated by arrows, between the wider side rolls 7.

Referring again to FIG. 2, in the operation of a continuous casting machine with an apparatus according to the present invention, liquid metal is poured into mold 4 and cooled by a suitable arrangement which may be, for example, an arrangement such as shown in my US. Pat. No. 3,610,322 of Oct. 5, 197]. As the metal is cooled in mold 4, a strand 12 is formed and emerges downwardly from mold 4. The strand 12 is initially formed as a shell with sides. such as 121; in FIG. 2, that become progressively thicker asstrand 12 moves downwardly but nevertheless are relatively thin and enclose a still liquid core 12c. Immediately below mold 4 and before strand I2 enters a secondary cooling zone, the strand 12 passes through the multi-sided passageway defined by'the rolls 7 and 8. As the convex rolls 8 engage the sides 12b of strand 12, the sides 12!; are each shaped to form a continuous concave arch. The strand 12 may then pass to a secondary cooling zone for solidifying the core in a manner conventional in this technology. The convex support and shaping rolls 8, for arching the narrower sides 12b of strand 12, may be used with an existing mold and wide side support rolls when modifying existing casting machines to incorporate the present invention.

The invention therefore provides an apparatus and casting procedure which produces a strand 12 having asmall concave arch on the opposite narrow sides 12a, but not limited to the narrow sides. This arch improves the total strength of the shell and especially the strength of the sidewalls 12b with the concave arch. This increase in strength will assure that bulging is prevented even if additional support for the sidewalls 12b is not provided beyond rolls 8. Therefore, it is satisfactory, normally, to support the strand 12 beyond rolls 8 only on the wide sides 12a, which remain flat. The thrust applied to arms 8a required to produce the arch is transferred into the rolls 7 supporting the strand 12 on the wide sides 12a. The same thrust also pushes the corners 14 of the strand 12 toward the outside so that they remain flat with the wide rolls 7 which provides a uniform strand thickness over the entire width of the strand 12. Defects such as the cracks 3 shown in FIG. 1 are avoided by the arrangement of rollers 7 and 8 shown in FIGS. 2 and 3, and safety precautions such as were necessary with casting machines according to the prior art, may be dispensed with.

From the foregoing detailed description of the present invention it has been shown how the features of the present invention have been provided in a preferred manner. However, modification and equivalents of the disclosed concepts such as readily occur to those skilled in the art are intended to be included in the scope of this invention. Thus, the scope of the invention is intended to be limited only by the scope of the claims such as are or may hereafter be, appended hereto.

The embodiments of the invention in which an exclusive property or privelege is claimed are defined as follows:

1. An apparatus for supporting and shaping a strand of continuously cast metal having a shell of solidified metal and a still liquid core of molten metal, said apparatus comprising:

a. a plurality of strand supporting rolls arranged to define a multi-sided strand passageway with at least a first pair of said rolls being of uniform diameter along its entire length, parallel and Spaced apart in mutually facing arrangement and a second pair of said rolls parallel to each other and arranged between the rolls of said first pair;

b. each roll of said second pair having an axial length less than the distance between the rolls of the first pair of rolls and each roll of said second pair is arranged with its axial ends spaced from the close ad- I jacent roll of the first pair; and

sitely facing strand surfaces to define a continuous concave arch.

2. An apparatus according to claim 1 in which said convex rolls are movable toward and away from each other between said first pair of rolls for forming concave arched side surface strands of different widths. 

1. An apparatus for supporting and shaping a strand of continuously cast metal having a shell of solidified metal and a still liquid core of molten metal, said apparatus comprising: a. a plurality of strand supporting rolls arranged to define a multi-sided strand passageway with at least a first pair of said rolls being of uniform diameter along its entire length, parallel and spaced apart in mutually facing arrangement and a second pair of said rolls parallel to each other and arranged between the rolls of said first pair; b. each roll of said second pair having an axial length less than the distance between the rolls of the first pair of rolls and each roll of said second pair is arranged with its axial ends spaced from the close adjacent roll of the first pair; and c. each roll of said second pair having equal end diameters smaller than a diameter midway between said end diameters and defining a convex peripheral surface, for supporting between said pair of rolls a continuous strand of continuously cast metal having a shell of solidified metal and a still liquid core and shaping the strand to form a pair of oppositely facing strand surfaces to define a continuous concave arch.
 2. An apparatus according to claim 1 in which said convex rolls are movable toward and away from each other between said first pair of rolls for forming concave arched side surface strands of different widths. 